The basic component of wire-drawing machines is the die through which wire or rod is drawn. The die does not remove any of the metal of the rod but uniformly reduces its cross-sectional area and at the same time improves the finish and physical properties. A block, comprising essentially a large motor driven spool, is positioned downstream of the die to pull the wire through the die by winding the wire around its outer circumference. In most cases, the wire or rod must be drawn through successive dies of progressively narrowing diameter so that the desired cross-sectional area can be achieved.
Before the advent of continuous machines, wire was drawn on drawing frames. These frames included a number of dies and blocks associated with each die. The length of wire of the desired diameter was produced by first drawing it through the largest die onto the block associated with that die and then once this process was completed, the wire was moved and drawn through the next die onto that die's block.
Continuous machines represent an improvement over the older wire-drawing frames. In these machines, the same length of wire is drawn continuously through a series of dies of decreasing diameter. Continuous wire-drawing machines are generally divided into two classes, cumulative and non-cumulative. Non-cumulative machines have a number of dies and blocks downstream of each die. Since the wire lengthens as it passes through the successive dies, each of the downstream blocks must be run at incrementally higher speeds while maintaining the necessary tensions to draw the wire through the blocks. The tensions are automatically controlled by providing dancers in between the blocks which sense tension on the wire. The speeds of the blocks are then automatically adjusted to maintain constant tensions.
The most common examples of a continuous cumulative-type wire-drawing machine are the multiple-draft double-block and overhead take-off (OTO) wire-drawing machines. These machines also have a number of dies and blocks downstream of each one of these dies. The blocks have a capability of dynamically accumulating small quantities of wire so that wire tension in the dies can be consistently maintained even as the wire length is increasing between the dies. The accumulation also allows cooling in between the dies so that the wire does not melt. The standard practice is that an operator controls the speeds of the blocks manually so that none of the blocks either runs out of nor accumulates too much wire.